The overall objective of the proposed project is to elucidate the role of taurine and Gamma-aminobutyric acid (GABA) in mammalian retina. More specifically, we plan to perform the following studies: 1. To identify GABA-containing and taurine-containing neurons and their processes and to analyze the synaptic circuitry of these neurons in retina by localizing their respective synthesizing enzymes, namely, L-glutamic acid decarboxylase (GAD) for GABA and cysteinesulfinic acid decarboxylase (CSAD) for taurine using light and electron microscopic (EM) immunocytochemical methods with specific anti-GAD and anti-CSAD sera, respectively. 2. To elucidate the mechanism by which the functions of GABA and taurine in retina are regulated. One such mechanism is the potentiation of GABA action by benzodiazepine (BDZP). Hence, the precise cellular and subcellular distribution of BDZP receptor and its endogenous ligands in retina will be determined with a special emphasis on the relationship between BDZP and GABA system. 3. To localize taurine- and GABA-accumulating and taurine- and GABA-receptive processes by EM autoradiography, following both in vivo and in vitro exposure of retina to radioactively-labeled GABA and taurine and their analogues. 4. To determine the developmental sequence of GABAergic system and taurine-containing neurons and the role of taurine and GABA in the development of retinal function. The following parameters will be analyzed at various developmental stages, e.g., in embryonic stages, newborn, during active synaptogenesis and at adult in order to determine the sequence of events that appears during retinal development: (a) the GABA- and taurine-synthesizing activities, namely, GAD and CSAD activities and their precise cellular and subcellular locations (presynaptic marker); (b) the GABA- and taurine-receptive sites (post-synaptic elements); (c) the GABA- and taurine-accumulating activities (uptake processes); and (d) the BDZP receptor activity and the level of the endogenous BDZP-like substance. In addition to the normal conditions, animals with photoreceptor dystrophy or animals treated with taurine-free diet, monosodium glutamate, or iodoacetate-L-malic acid mixture will also be examined.